Autolinking

Autolinking is the mechanism that scans your dependencies for native code and adds it to the iOS and Android builds automatically. Install a library such as react-native-mmkv, rebuild, and its native module is available without touching Xcode or Gradle files.

It works at build time, on both platforms:

• iOS — the Podfile calls use_native_modules! (and use_expo_modules! in Expo projects), which finds each library’s podspec in node_modules and hands it to CocoaPods.
• Android — the Gradle settings call into the same discovery logic, include each library as a Gradle project and generate the code that registers its packages.

There are two implementations: the React Native Community CLI’s, configured through react-native.config.js, and Expo’s, which also discovers modules built with the Expo Modules API. Expo projects use both.

The key point newcomers miss: autolinking only runs when the native app is built. Installing a native library and reloading JavaScript is not enough. You must rebuild:

npx expo run:ios       # or a new development build
cd ios && pod install  # bare React Native, then rebuild

Skip that step and you get an error like TurboModuleRegistry.getEnforcing(...): 'X' could not be found, or a “native module is null” message from older libraries. For the same reason a library with custom native code cannot work in Expo Go; it needs a development build.

You can opt a package out per platform in react-native.config.js:

module.exports = {
  dependencies: {
    'some-library': { platforms: { ios: null } },
  },
};

Before autolinking, every install meant manually editing the Xcode project, settings.gradle and MainApplication, which is why old READMEs still mention react-native link.